Measurement of charge of Cu and O in YBa2Cu3Oy by energy-filtering convergent-beam electron diffraction

Large-angle convergent-beam electron diffraction (CBED) patterns were obser ved from small areas in nanometer scale in YBa2Cu3Oy (Y123), using a new tr ansmission electron microscope (TEM) JEM-2010FEF. An energy filter of omega type was used to subtract background intensities caused by inelastically s cattered electron. Specimens were cooled with a liquid nitrogen stage to su ppress thermal diffuse scattering that cannot be eliminated well by the ene rgy filter. In order to measure specimen thickness, electron energy loss sp ectra were also measured from the same areas where CBED patterns were recor ded. Charges of Cu and O on CuO chains and CuO2 planes, and charge of O on Ba-O planes were determined by analyzing the intensities of CBED patterns w ith the dynamical theory of electron diffraction. The obtained values are C U2.0+ and O1.65- On CuO chains, Cu2.2+, O1.98- on CuO2 planes and O2.0- On BaO planes. The present results indicate that the energy-filtering CBED tec hnique is useful for determination of charge distribution along the z-direc tion in Y123. (C) 2000 Elsevier Science B.V. All rights reserved.